1. Field of the Invention
This invention relates to valves for the control of fluid flow and, in particular, to regulator valves for installation in gas supply pipes.
2. Description of the Prior Art
In a control system governing fluid flow, out-of-balance forces across the head of the control valve will degrade the performance of the system. Such out-of-balance forces occur due to differences in area of the upstream and downstream faces of the valve head, pressure differences across the valve and fluid momentum due to impingement of the fluid on the valve head.
Various methods have been proposed to reduce the effects of out-of-balance forces. One technique is to employ a dual-ported valve. Another is to allow fluid from opposite sides of the valve head to communicate with a compensating piston attached to the same spindle.
Both of these techniques exhibit disadvantages. For example, with the first technique the assembly is rather bulky and requires the two valves to close precisely simultaneously, and with the second technique, the pressure will vary across the face of the valve, therefore, transferring pressure from a specific location will not provide accurate compensation. In such conventional regulator valves, when closed or almost closed, the areas of the upstream and downstream faces of the piston differ in addition to the difference due to the cross-sectional area of the spindle. Complex passageways are required to trasfer pressure from the valve head to the balance piston.
In order to overcome these disadvantages, a novel valve for control of fluid flow has been devised.